Small molecules form the foundation of our toolbox of clinically used therapeutics as well as chemical probes for studying biological systems. However, their applications can be complicated by a lack of cell-type selectivity for the cell subsets responsible for disease. This is particularly true of compounds used to treat hematologic cancers, most of which are natural product derivatives that target rapidly dividing cells ? including both cancerous cells and healthy hematopoietic cells, which in healthy individuals generate 3x1011 new blood cells each day. An additional limitation of this approach is that antiproliferative therapies fail to eliminate the relatively quiescent leukemic stem cells (LSCs), which survive therapy and often lead to recurrence. Our group recently discovered that two families of glycosylated polyketides compounds produced by the soil bacteria Nocardiopsis FU-40 exhibit striking selectivity for distinct subsets of cells found in patients with acute myeloid leukemia (AML). The ciromicins appears to be selectively cytotoxic towards immature myeloid leukemia cells and leukemic stem cells, while the apoptolidins selectively target mature lymphocytes. We hypothesize that this represents selective targeting of hematopoietic cells at defined stages of maturation ? differentiation dependent targeting. The proposed project will assess the relative cell-type selectivity of these compounds in normal and abnormal hematopoiesis and attempt to define the molecular basis of their observed selectivity. In Aim 1, we will investigate the extent to which the ciromicins and apoptolidins selectively target developmentally defined hematopoietic cell subsets. With the help of our collaborators, we will use mass-cytometry to comprehensively characterize the hematopoietic hierarchy in healthy hematopoiesis, myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML), and how it is perturbed by treatment with the ciromicins and apoptolidins. In Aim 2, we will attempt to identify the target(s) of the ciromicins and apoptolidins using affinity purification coupled to quantitative proteomics. This approach has the potential to reconcile the observed selectivity of the apoptolidins with their reported mechanism which remains an open question in the field, and will provide the first in depth study of the mechanism of action of the ciromicins. As the phenotype induced by these compounds suggests that they are capable of selectively targeting the subsets of cells responsible for disease, this study may define new targets for understanding and treating clonal hematopoietic disorders. Together, these aims will provide a comprehensive understanding of the mechanism of action of glycosylated polyketides at both single cell and molecular resolution, while simultaneously providing an ideal training and mentorship environment for my development as a physician-scientist.